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Journal of Applied Physics

Issue 2 • Date Jan 1995

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Displaying Results 1 - 25 of 78
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Growth and optical properties of nanometer‐scale GaAs and InAs whiskers

    Page(s): 447 - 462
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    The growth process, crystal structure, and optical properties of ultrathin GaAs and InAs wires (whiskers) as thin as 15–40 nm and about 2 μm long are reviewed and discussed. Experimental results for growing whiskers using Au as a growth catalyst during metalorganic vapor phase epitaxy (MOVPE) and the shape and growth direction of whiskers provide new insight into growth control of GaAs and InAs whiskers. The crystal structure of whiskers, Au behavior during MOVPE, and their growth mechanism are reviewed and discussed on the basis of transmission electron microscopic analysis. The photoluminescence spectra of GaAs wires are compared with those of a GaAs epitaxial layer, and the effect of surface treatment on the luminescence peak energy shift is discussed. The time dependent photoluminescence of GaAs wires is also discussed. The application of GaAs whiskers to light emitting devices is reviewed because a semiconductor wire structure employing quantum size effects is a very important element of electronic and optical devices. © 1995 American Institute of Physics. View full abstract»

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  • Control of emittance growth due to mismatches in accelerators that use stellarator transport

    Page(s): 463 - 473
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    In the spiral line induction accelerator, an intense electron beam is transported along an open‐ended beam pipe that makes multiple passes through the accelerating cavities. In the straight sections of the beam line, solenoidal focusing is used; in the bends, an l=2 stellarator field is used. At the solenoid/stellarator transition, where the beam equilibrium changes, a mismatch can occur, exciting oscillations of the beam envelope. Numerical simulation is used to show that the frequency, damping rate, and emittance growth associated with these oscillations are sensitive to nonlinear space‐charge forces that depend significantly on the radial profile of the beam. Comparisons between simulation and experimental results illustrate this sensitivity. It is shown that mismatch oscillations can be avoided by using a single thick quadrupole lens at the solenoid/stellarator transition. Simulation and experimental results show excellent agreement. View full abstract»

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  • Spectroscopic and laser investigations of Mn5+:Sr5(VO4)3F

    Page(s): 474 - 480
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    Mn:Sr5(VO4)3F has been investigated as a laser material for operation near 1200 nm. Absorption and emission spectra are consistent with Mn5+ substitution into the distorted tetrahedral V5+ sites of this apatite crystal. Emission is almost entirely from the 1E state, resulting in a room‐temperature fluorescence lifetime of 475 μs. Together with a peak stimulated emission cross section of about 1×10-19 cm2 and strong, broad absorption bands, this is attractive for lamp‐ or diode‐pumped laser operation. However, the 1E emission makes Mn:Sr5(VO4)3F a three‐level system. Laser operation has been demonstrated at room temperature, but the efficiency is lower than expected. Single‐pass gain measurements and saturable absorption and fluorescence data indicate that the primary difficulty is excited‐state absorption at the pump wavelength. This absorption is very broad, and is probably due to 1T1 and 1T2 excited states. © 1995 American Institute of Physics. View full abstract»

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  • Photochromic command surface induced switching of liquid crystal optical waveguide structures

    Page(s): 481 - 487
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    We report on optical waveguide structures containing a thin liquid crystal (LC) film held between two photochromic command surfaces. The command surfaces consist of three monomolecular layers of a polymer with azobenzene side chains deposited according to the Langmuir–Blodgett–Kuhn technique. When exposed to light of appropriate wavelength, the command surfaces undergo a trans↔cis photoisomerization process that induces a reversible change in the liquid crystalline orientation. Such an orientation change of the LC alters the optical properties of the optical waveguide. We present experiments on the dynamics of the LC orientation process. The transition is shown to be continuous, with the degree of orientation dependent on the ratio of the cis‐trans chromophore concentration ratio in the command surface. © 1995 American Institute of Physics. View full abstract»

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  • Competition between carrier concentration and temperature influences on gain as means for improving modulation response of semiconductor laser

    Page(s): 488 - 493
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    Concentration and effective temperature of carriers are established to compete in their influences on the band‐edge dielectric function of an active semiconductor medium under the lasing conditions. This competition is shown as capable of suppressing the relaxation oscillations and wavelength chirping in the modulation response of a semiconductor laser, provided the carrier injection and carrier heating are combined in a suitable way. The problem of how to combine them is studied under the small‐signal approximation assuming that modulation signal can be imposed on both the injection current and energy flux flowing into the active layer. All the numerical results relate to single‐frequency 1.55 μm GaInAsP/InP laser. © 1995 American Institute of Physics. View full abstract»

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  • Thermal diffusivity/conductivity in SiAlON ceramics

    Page(s): 494 - 496
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    Thermal diffusivity and conductivity of ceramic materials in a system of Si3N4‐SiO2‐Al2O3‐AlN composed of α and β SiAlON (which is well known as duophase SiAlON ceramics) are investigated. Single‐phase β‐SiAlON ceramic has a thermal conductivity of 12.44 W/m K. The thermal conductivities of SiAlON ceramics decrease linearly with increasing content of α phase and can be best described by the following equation: K=12.46–0.043 f, where f is the weight percentage of α‐SiAlON content and K is the thermal conductivity of SiAlON ceramics. The thermal conductivity of single‐phase α‐SiAlON was then estimated to be ∼8.16 W/m K, which is in excellent agreement with the literature reported values, ∼8.4 W/m K. This estimation is also close to the value, 8.22 W/m K, obtained by using Bruggeman’s variable dispersion theory. The temperature dependence of the thermal conductivity of duophase SiAlON ceramics varies with α and β phase contents in the materials. © 1995 American Institute of Physics. View full abstract»

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  • Role of the chamber wall in low‐pressure high‐density etching plasmas

    Page(s): 497 - 504
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    Ultraviolet‐adsorption spectroscopy has been used to examine how the chamber wall affects the concentration of gas‐phase reactants in high‐density etching plasmas. This technique was employed to detect CF2 in an inductively coupled discharge used for the selective etching of silicon dioxide relative to silicon nitride and polycrystalline silicon (polysilicon) films. In plasmas containing C2F6 and CF4, the concentration of CF2 depends strongly on the applied power and operating pressure as well as the amount of polymer on the walls of the chamber. Changes in the conditioning of the chamber during the etch process cause significant variations in the concentration of CF2 in the discharge. The selectivity of etching SiO2 relative to Si3N4 films closely follows the concentration of CF2 under a variety of plasma operating conditions. The ability to measure a fundamental plasma characteristic that reflects the level of conditioning of the chamber is an important step in the real‐time monitoring of a reactor parameter that currently can only be determined from postprocess measurements. © 1995 American Institute of Physics. View full abstract»

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  • Spatially and temporally resolved absolute O‐atom concentrations in etching plasmas

    Page(s): 505 - 511
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    The detection of atomic O by two‐photon‐allowed laser‐induced fluorescence is implemented to obtain the spatial distribution and the temporal evolution of oxygen atoms in a 10 MHz parallel‐plate rf discharge. Absolute concentrations are determined via a titration technique for intensities typically found in 20–100 W, 0.1–3 Torr O2 discharges, and are in the range 4–30×1014 atoms/cm3. The spatial O distribution after initial turn on of the discharge is rather uniform, indicative of a uniform production of O atoms throughout the interelectrode space. Furthermore, the decay of the O concentration reveals information about the reaction of O atoms with surface materials in the plasma environment, while the rise of the population indicates a time‐dependent production rate. The dependence of the O‐concentration rise and decay rates on discharge pressure, power, and gas composition is explored. © 1995 American Institute of Physics. View full abstract»

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  • Effect of oxygen on the electrical and optical properties of In0.5Ga0.5P grown by liquid‐phase epitaxy

    Page(s): 512 - 516
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    The effect of oxygen on the electrical and optical properties of In0.5Ga0.5P epitaxial layers grown on (100) GaAs by liquid‐phase epitaxy has been investigated by adding Ga2O3 to the growth melt. As the amount of Ga2O3 increases, the carrier concentration at 300 K decreases from 4×1016 to 4×1015 cm-3 and the Hall mobility at 77 K increases from 2400 to 4000 cm2/V s. The photoluminescence at 17 K shows that the peak intensity of an extrinsic transition in the In0.5Ga0.5P layer is reduced when Ga2O3 is added to the growth melt. These facts indicate that the main effect of Ga2O3 is the reduction of impurity concentration in the growth melt. In the In0.5Ga0.5P layer grown from the Ga2O3‐added growth melt, the same deep trap, with an activation energy of 0.29 eV, as in an undoped layer is observed but the trap density is decreased. This implies that the deep trap is not due to a simple intrinsic defect, but related to an impurity. © 1995 American Institute of Physics. View full abstract»

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  • Microstructural measurements of amorphous GeTe crystallization by hot‐stage optical microscopy

    Page(s): 517 - 521
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    Time‐resolved hot‐stage transmission optical microscopy is used to characterize the nucleation and growth kinetics of amorphous GeTe thin‐film crystallization. This technique provides experimental measurements of the fraction crystallized, the number of crystallites, and the crystallite size as a function of annealing time and temperature. The fraction‐crystallized data are modelled using the Johnson–Mehl–Avrami formalism to give an Avrami exponent of 4, consistent with previous measurements via time‐resolved reflection/transmission methods. Microstructural measurements provide sufficient data to deconvolute the individual contributions of nucleation and growth to this exponent. This work shows that crystallization of these films proceeds by nucleation at an increasing rate due to transient effects with isotropic two‐dimensional growth in the film plane. © 1995 American Institute of Physics. View full abstract»

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  • On the two‐state microstructure of nanocrystalline chromium

    Page(s): 522 - 527
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    High‐angle neutron powder diffraction was used to investigate the grain size dependence of the Debye–Waller parameter (DWP) of nanocrystalline and coarse‐grained chromium samples. The DWP measured at 20 K depends linearly on inverse grain size and is consistent with a two‐state model in which defects with short‐ranged displacement fields are present in differing concentrations in two distinct microstructural regions within individual grains. One possible model microstructure consists of grain boundary and free surface regions with significantly larger concentrations of point defects than in grain interiors. Evidence is also seen for an enhancement of the temperature‐dependent component of the DWP of chromium with decreasing grain size, indicating different behavior than seen previously for nanocrystalline palladium. © 1995 American Institute of Physics. View full abstract»

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  • Relation between lattice strain and anomalous oxygen precipitation in a Czochralski‐grown silicon

    Page(s): 528 - 532
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    Spatial fluctuations of lattice strain in an as‐grown Czochralski‐grown silicon wafer, in which a ring‐shaped region of densely distributed oxidation‐induced stacking faults appears after oxidation thermal treatment, are measured by double‐crystal reflection topography with synchrotron radiation. The measured lattice strain is isolated into local variations in lattice dilation and inclination angle from an average plane. The variation profile of the lattice spacing shows a small valley in the ring‐shaped region, while showing a peak just outside the ring‐shaped region. The relation between the lattice strain and anomalous oxygen precipitation is discussed. © 1995 American Institute of Physics.   View full abstract»

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  • Solid‐state reactions in binary mixtures of nanometer‐sized particles

    Page(s): 533 - 539
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    Solid‐state reactions in mixtures of nanometer‐sized Cu and Zr as well as Ni and Zr crystallites—produced by inert‐gas condensation followed by in situ compaction—have been investigated by x‐ray diffraction and thermal analysis. Nanocrystalline particle mixtures and multilayered samples showed qualitatively the same behavior: A solid‐state amorphization reaction occurs in NixZr1-x samples but not in CuxZr1-x. The results are discussed in the framework of a heterogeneous nucleation and growth process for the amorphous phase. Comparison with results from ball‐milling experiments and mechanically prepared multilayers reveals the significance of additional external driving forces. © 1995 American Institute of Physics. View full abstract»

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  • Systematic study of PbTe (111) molecular‐beam epitaxy using reflection high‐energy electron‐diffraction intensity oscillations

    Page(s): 540 - 552
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    Molecular beam epitaxy of PbTe on BaF2 (111) is studied using reflection high‐energy electron diffraction (RHEED). The influence of growth parameters (substrate temperature and growth rate) on surface kinetics and the steady‐state growth surface morphology is investigated employing dynamical RHEED measurements (RHEED oscillations). For a well adjusted stoichiometric PbTe beam flux composition, two‐dimensional layer‐by‐layer growth can be achieved from substrate temperatures as high as 410 °C down to temperatures below 95 °C, with a maximum number of 230 RHEED oscillations observed at substrate temperatures in the 160 °C range. At temperatures above 400 °C, the growth kinetics start to be modified by PbTe reevaporation from the layer surface. The dependence of the RHEED oscillations on substrate temperature and growth rate indicates the importance of adatom surface diffusion for the surface morphology developed under steady‐state growth conditions, and for all growth conditions, a close correlation between steady‐state growth surface step density and damping of RHEED oscillations is observed. Furthermore, it is shown that even very small changes in the beam flux composition have a dramatic influence on the RHEED intensity oscillations as well as the surface processes involved in the growth. With only a small additional Te2 flux used for the growth, an abrupt growth mode transition from layer‐by‐layer to step flow growth is induced. This is the first evidence that PbTe molecules impinging on the layer surface do not dissociate upon adsorption, but remain in a molecular state until incorporated in the crystal lattice. © 1995 American Institute of Physics. View full abstract»

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  • Distribution of SiO2 precipitates in large, oxygen rich Czochralski‐grown silicon single crystals after annealing at 750 °C

    Page(s): 553 - 562
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    The defects due to oxygen precipitation in Czochralski grown silicon single crystals annealed for 216 h at 750 °C and with oxygen concentration varying between 18 and 12×1017 atoms per cm3 (according to DIN 50438) were studied by means of small angle neutron scattering and γ‐ray diffractometry probing the same volume elements in the sample. The size and the shape of the SiO2 precipitates were determined by means of small angle neutron scattering. In the center of the disk‐shaped sample of 10 cm diameter one finds spherical precipitates with a radius of ≊20 Å, at the border the precipitates are of plate‐like shape, ≊146×146×41 Å in dimension. The k‐space distribution of the diffuse scattering caused by the strain field of the SiO2 precipitates has been determined by means of a double‐crystal diffractometer and 316 keV γ radiation. Modeling with Huang and Stokes–Wilson theory suggests that the relatively small SiO2 precipitates are loosely bound in larger clusters with a radius of ≊2000 Å in which the crystal matrix is strongly distorted. With the γ‐ray diffractometer operated in the single‐crystal mode the thickness dependence of the integrated reflecting power was measured from which the static Debye–Waller factor for the 2 2 0 reflection is determined using statistical dynamical theory. The results confirm qualitatively the cluster model. In the center of the sample the size of the precipitates could be calculated by additional measurement of the static Debye–Waller factor of the 4 4 0 reflection. The result is in excellent agreement with the small angle neutron scattering data. Combining all the experimental data taken in the oxygen rich center of the annealed silicon crystal the average distance between the centers of the SiO2- precipitates in the clusters is ≊80 Å and the distance between the large clusters is ≊40 000 Å. © 1995 American Institute of Physics. View full abstract»

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  • Scanning tunneling microscope crystallography of titanium silicide on Si(100) substrates

    Page(s): 563 - 571
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    A scanning tunneling microscope (STM) in ultrahigh vacuum has been used to investigate the growth, morphology, and surface atomic structure of ultrathin titanium silicide films on Si(100) substrates. Microstructural considerations have been used to identify various stages of the silicide growth. Methods for STM crystallography have been developed and used to identify possible epitaxial silicide/silicon relationships based on morphological considerations. Atomic resolution images of a titanium silicide crystallite have identified a 2×2 silicon termination of a C54‐TiSi2(111) surface. It is shown that unambiguous identification of epitaxial relationships requires images of the atomic structure of the silicide crystallite surfaces in addition to morphological information. © 1995 American Institute of Physics. View full abstract»

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  • Dynamics of selective reflections of cholesteric liquid crystals subject to electric fields

    Page(s): 572 - 576
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    In this paper we report on the time behavior of the apparent pitch of a cholesteric mixture undergoing a step‐like dc electric field applied parallel to the helical axis. We show that the relative variation of the apparent pitch Δλ(t)/λ0 decreases from the initial value to negative ones (λ≪λ0) by two different characteristic times and tends finally to a saturation value with Δλ/λ0≪0 after a long time. An attempt to explain this phenomenon in a (semi‐)quantitative way has been made by considering relaxation mechanisms on different spatial scales. © 1995 American Institute of Physics. View full abstract»

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  • Oxide growth, refractive index, and composition depth profiles of structures formed by 2 MeV oxygen implantation into silicon

    Page(s): 577 - 586
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    Single‐crystal Si has been implanted with O+ ions at 2 MeV energy, to doses from 0.1 to 2×1018 O+ cm-2 and at substrate temperatures between 90 K and 700 °C. Infrared reflection spectra in the transparent region 1500–7000 cm-1 were measured and interference fringes were observed. A detailed theoretical analysis of the interference fringes yields refractive index profiles which provide accurate measurements of the range and straggle of the implanted ions, the Si overlayer crystallinity, and the oxygen concentration depth profile. The implantation temperature influences the crystallinity of the Si overlayer but not the oxygen distribution. The measured range parameters are in agreement with theory. The 2 MeV results are compared to results from 200 and 90 keV implants, which show that the method is applicable for a wide range of separation by implantation of oxygen structures. Rutherford backscattering spectroscopy and ion channeling results are in good agreement with the infrared results. It is concluded that infrared spectroscopy is the most convenient and inexpensive nondestructive technique to investigate structures formed by MeV and lower‐energy O+ implantation. © 1995 American Institute of Physics. View full abstract»

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  • Fractals in annealed Ge‐Au/Au bilayer films

    Page(s): 587 - 590
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    Ge‐22 at. %Au/Au bilayer films annealed at various temperatures have been observed by transmission electron microscopy. The as‐deposited bilayer film is composed of crystalline Ge,Au and metastable Ge0.4Au0.6 phases. The Au grain size is nonuniform, and no amorphous Ge is observed. During annealing at 60–350 °C, patterns with several wide branches are generated that are different from the dense branching fractals induced by crystallization of amorphous Ge in a‐Ge/Au films. The fractal dimension of the pattern (measured by the box‐counting method) increases with the annealing temperature. The agglomeration of small Au grains to coarse Au grains in the Ge‐Au/Au bilayer film may be the mechanism for the fractal structure formation. © 1995 American Institute of Physics.   View full abstract»

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  • Contribution of the x‐ray absorption spectroscopy to study TiO2 thin films prepared by ion beam induced chemical vapor deposition

    Page(s): 591 - 597
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    TiO2 thin films have been prepared and their structure analyzed by XRD at grazing angles and x‐ray absorption spectroscopies (EXAFS/XANES). The deposition method is an ion beam induced chemical vapor deposition procedure (IBICVD) consisting of the bombardment of a substrate with accelerated O+2 ions while the vapor of a volatile metallic precursor is directed on its surface. The structure of the films was dependent on the type of substrate (glass, fused quartz, and sapphire) and on the conditions used for their preparation (temperature of substrate and beam energy of 1 or 10 keV). Thus, while on glass and silica/sapphire, an amorphous structure is formed when the substrate is at 300 K during preparation, a rutile‐rich structure is obtained if the substrate is at 573 K during deposition or, even to a larger degree, when using ions of 10 keV. The amorphous structure of the films grown on glass yield 100% anatase after calcining at 773 K. On sapphire, the crystallization was less perfect and besides anatase, rutile and amorphous phases were detected after calcination at that temperature. The films prepared at 573 K or with O+2 ions of 10 keV yield after calcining a well ordered structure of rutile. A detailed analysis of the EXAFS and XANES spectra has permitted a better characterization of the amorphous and crystalline phases in the films and provided a better understanding of the crystallization processes during calcination. The contribution of the different factors controlling the crystallization of the films is discussed. © 1995 American Institute of Physics. View full abstract»

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  • Crystal plasticity simulations of thermal stresses in thin‐film aluminum interconnects

    Page(s): 598 - 606
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    Thermal stresses that develop in aluminum interconnects upon cooling from an annealing temperature are investigated using crystal plasticity theory. The crystal plasticity model is implemented assuming either isotropic hardening or a physically based hardening model developed for single crystals. The dependence of the predicted thermal stresses on crystal orientation and on interconnect aspect ratio is examined. The results are compared with recent observations of electromigration‐induced transgranular voids to ascertain the contribution of the thermal stresses in the failure of aluminum interconnects. The analysis clearly demonstrates the necessity of accounting for all slip systems when modeling the effects of texture in single‐crystal thin films. In addition, the calculations suggest that proper consideration of the hardening description is necessary for accurate predictions of thermal stresses. © 1995 American Institute of Physics. View full abstract»

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  • In situ studies of the crystallization kinetics in Sb–Ge films

    Page(s): 607 - 613
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    The crystallization process in SbxGe1-x alloy films has been observed during in situ annealing in a transmission electron microscope. Results are presented for two films with x=0.89 (89 at. % Sb) and x=0.71 (71 at. % Sb), which lie on either side of the eutectic composition (x=0.85). In the former films radial crystals are observed to grow rapidly from discrete nuclei, whereas in the latter films the crystallization process occurs through a near‐planar front. In addition, quantitative data obtained from these experiments show that the Sb0.89Ge0.11 films have a higher activation energy for crystal growth and a lower temperature for the nucleation of crystals. Significant differences are observed between the crystallization processes for the two films studied, with the Sb0.89Ge0.11 film showing better potential for development as an ultrafast optical phase‐change storage medium. © 1995 American Institute of Physics. View full abstract»

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  • Activation energy for CoSi and CoSi2 formation measured during rapid thermal annealing

    Page(s): 614 - 619
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    The activation energies, Ea’s, for CoSi and CoSi2 formation were determined using in situ resistance measurements during rapid thermal annealing. Co films were evaporated on undoped polycrystalline Si (poly‐Si) and single‐crystal Si on sapphire (SOS) substrates. The resistance was monitored for heating rates from 1 to 60 °C/s up to 900 °C. There was significant thermal lag between the samples and thermocouple embedded in the susceptor wafer for heating rates greater than 20 °C/s. The thermal lag was quantified by melting Au‐Si, Al‐Si, and Ag‐Si eutectics, and shown to be consistent with finite element modeling. The Ea’s determined from Kissinger plots for heating rates ≤20 °C/s were 2.09±0.11 and 2.03±0.08 eV for CoSi formation and 2.91±0.22 and 2.81±0.23 eV for CoSi2 formation, for Co/poly‐Si and Co/SOS samples, respectively. © 1995 American Institute of Physics. View full abstract»

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  • Comparison of the radiation resistance of electron irradiated indium phosphide grown by metal‐organic chemical‐vapor deposition and liquid encapsulated Czochralski

    Page(s): 620 - 627
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    Electrical characterization has been carried out on electron irradiated InP grown by metal‐organic chemical‐vapor deposition (MOCVD) and liquid encapsulated Czochralski (LEC), through I–V (–T), C–V, deep level transient spectroscopy (DLTS) and admittance spectroscopy measurements and the resistance to electron radiation for these two materials has been compared. It was found that MOCVD‐InP was more resistant to electron radiation than LEC‐InP, as demonstrated by the lower carrier removal rate and change of series resistance in the MOCVD‐InP diodes as a result of electron radiation. The introduction rates for the dominant hole defects H3 and H4 and for additional electron defect states were found to be similar for both materials, but were insufficient to explain the degree of degradation of solar cell efficiency incurred by these known defects. A new defect, HD1, has been found to be responsible for the high carrier removal rate and the introduction of a large series resistance which accounts for the difference of radiation hardness between these two materials. The results again show that the dominant irradiation defects in InP are not the defects H3 and H4 as is usually accepted, but the new found defect HD1, which was undetected by the DLTS technique. © 1995 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory